There is no difference amongst those who decided to accept and work with the Khabar al-Wahid (1) in matters of Shari’ah that it must come through a ‘Adl, in our madhab ‘Adl means that the narrator must have a correct belief in Usool and Furu’u, that he must not be from a corrupt madhab according to the proofs, that he must not commit disobedience and evil deeds apparently. This means that we must not work with any of the narrations by the Waqifah of Musa bin Ja’afar (as) who believe that he was a Mahdi and all those after him are liars, this is clear kufr, such as al TaTari and ibn Sama’ah and such people which we cannot count as to their large numbers. The majority of our Fiqh or all of it is related to narrations from the Waqifah, whether they narrated the Hadith from someone or someone narrated it from them. Also others such as the Ghulat (2), the Mukhammisah (3), the people of Hulul (4) and they are too many to count “Or from a Qummi who is a Mushabbih or a Mujabbir (5), and all qummies with no exceptions except for Ibn Babaweih are Moushabihah and Moujabirah, their books all bear witness to this clearly. So what narration is safe from having in its chain a Waqifi or a Ghali or a Qummi who is a Mushabbih and a Mujabbir.”

Source: Rasael al-Shareef al-Murtada 3/310.

(1) What is narrated through one narrator.
(2) Extremist Shia who commit Ghulu and the Shia definition of Ghulu changes with the passing of time, this sect attributes divine features to ‘Ali, although many Twelvers in our days do this so ponder.
(3) Shia sect that believed that Allah came in the form of Muhammad, ‘Ali, Fatima, Hassan, Hussein.
(4) Those who believe Allah can appear in a specified physical form.
(5) Shia sects such as al-Bayaniyah and al-Sabaiyyah and others, they liken the creator to the creation.

Sheikh al-Taefa al-Tusi says: “Many of the authors from our companions and those who wrote the Usool have adopted corrupt Madhabs although their books are accepted.”

Source: al-Fihrist pg 2.

Basically if the Shia want to apply the proper science based on the ‘Adalah, then a big part of their Madhab would collapse as they rely on the narrations by people of corrupt madhabs whom they themselves deem as Kouffar.